Use Postgres peer authentication by default

Author: jacobvosmaer

config/database.yml.postgresql

@@ -6,7 +6,7 @@ production:
   encoding: unicode
   database: gitlab_ci_production
   pool: 5
-  username: postgres
+  username: gitlab_ci
   password:
   # host: localhost
   # port: 5432

doc/installation.md

@@ -76,8 +76,8 @@ You can use either MySQL or PostgreSQL.
     # Login to PostgreSQL
     sudo -u postgres psql -d template1
 
-    # Create a user for GitLab. (change $password to a real password)
-    template1=# CREATE USER gitlab_ci WITH PASSWORD '$password';
+    # Create a user for GitLab. We do not specify a password because we are using peer authentication.
+    template1=# CREATE USER gitlab_ci;
 
     # Create the GitLab production database & grant all privileges on database
     template1=# CREATE DATABASE gitlab_ci_production OWNER gitlab_ci;
@@ -129,8 +129,8 @@ You can use either MySQL or PostgreSQL.
 
     # postgres
     sudo -u gitlab_ci -H cp config/database.yml.postgresql config/database.yml
- 
-    # Edit user/password
+
+    # Edit user/password (not necessary with default Postgres setup)
     sudo -u gitlab_ci -H editor config/database.yml
 
     # Setup tables